ERK-1,2 and p38 MAPK activity assays in lysates of HUVECs treated with vWF. HUVECs were treated with 0 to 6 μg/ml vWF for four hours. Phosphorylated p38 MAPK and ERK-1,2 were immunoprecipitated from HUVEC lysates and their enzymatic activities were analyzed using their specific substrates, ATF-2 and Elk-1, respectively. (a) Shows representative Western blots of phospho-ATF-2 and phospho-Elk-1. (b) Shows the results of densitometric analysis of Western blots of phosphorylated ATF-2 (black circle) and Elk-1 (white circle). Data are shown as mean ± SD of three independent experiments.